PLC Ladder Diagrams Rules

PLC Ladder Diagrams Basic Rules

  1. Identify Power Loads & respective Final Control Element Loads.
  2. Identify Control Loads & Indication Loads
  3. Identify Power Supply and Control supply
  4. Draw Power Circuit with protection and operation features included
  5. Draw control circuit
  6. Both circuits should show switching contacts in their Normal Status
  7. Do not connect Loads in series
  8. Switching unit can have switches in parallel &/or series with each other
  9. Switching unit must be in series with load

A load may have more than one switching units connected parallel with each other but in series with the load
Ladder diagrams are specialized schematics commonly used to document industrial control logic systems. They are called “ladder” diagrams because they resemble a ladder, with two vertical rails (supply power) and as many “rungs” (horizontal lines) as there are control circuits to represent.